NICKEL MOLYBDATE AS PRECURSOR OF HDS CATALYSTS - EFFECT OF PHASE-COMPOSITION

Sulfided alpha- and beta-NiMoO4 have been employed as model HDS cataly sts, aiming to investigate the effect of phase composition of the prec ursor mixed oxide on the physicochemical characteristics and activity of the sulfides. Both sulfides are highly amorphous or microcrystallin e, and could not be differentiated by means of XRD. The differences in BET area were also found to be minimal. However, it was found by mean s of TPR that the stable alpha-isomorph is reduced at lower temperatur es than the unstable beta-phase in both the oxidic and sulfided states . Sulfided beta-NiMoO4 was found to be a better catalyst for the HDS o f thiophene than the sulfided alpha-isomorph. This could be related to the higher stability of the former in H-2, as decomposition of the ac tive, amorphous Ni-Mo-S structures results in less active and more cry stalline phases, as found by XRD.